Field of the Invention
The present invention relates generally to the field of immunology and vaccine development. More specifically, the present invention provides an immunogenic composition, comprising a lipopolysaccharide vaccine and a Toll-like receptor 9 (TLR9) agonist and its use in the prevention and treatment of sepsis and infection with biodefense agents.
Description of the Related Art
Gram-negative bacteria are causative agents of many life-threatening ailments which include pneumonia, plague, tularemia, meliodosis and sepsis. These bacteria can also be used as biowarfare agents. Gram-negative bacterial sepsis is a serious complication in patients residing in intensive care units (ICUs), undergoing abdominal surgery or incurring trauma or burns and in patients that develop prolonged neutropenia. Although antibiotic therapy plays an important role in limiting the incidence of this complication, there has been little change in the mortality of this condition once it develops as seen in the last few decades. Consequently, there has been considerable effort to devise new therapies to complement the advances in supportive care and anti-microbial therapy. An example of such therapy that is being explored is the use of vaccines.
Active or passive immunization with Gram negative bacterial endotoxin (or lipopolysaccharide, LPS) protects against lethal infection upon subsequent exposure to the same serotype of the organism from which the lipopolysaccharide was derived (known as “homologous protection”). However, such a vaccine does not protect against Gram-negative bacteria from other serotypes of that same species of bacteria or from different Gram-negative bacterial species (i.e. “heterologous” bacteria). This is because the antibody thus elicited is directed against the outermost sugars of the lipopolysaccharide molecule, each of which is specific for that one serotype.
In contrast, the core portion of the lipopolysaccharide, also called “core glycolipid”, is widely conserved among many different Gram-negative bacteria such that antibodies directed against this core glycolipid provide heterologous protection i.e. protect against subsequent challenge with a wide spectrum of clinically relevant Gram-negative bacterial pathogens (1-2). Antibodies against an even more widely conserved region of the lipopolysaccharide molecule, the lipid A, have not been shown to be protective in either experimental or clinical studies of sepsis.
The ability of one such vaccine comprising lipopolysaccharide of an Rc chemotype mutant of E. coli 0111:B4 (E. coli J5) to provide protection against an array of Gram negative bacteria was examined in a previous study. The preparation of such a vaccine involved detoxification of the lipopolysaccharide first by alkaline treatment to cleave ester-linked fatty acids of the lipid A component of lipopolysaccharide followed by non-covalent complexing with the outer membrane protein (OMP) of Neisseria meningitidis Group B. This dLPS-J5/OMP vaccine protected against lethal gram-negative bacterial sepsis when administered either actively as a vaccine preventive strategy or passively as immune plasma in a neutropenic rat model of Pseudomonas sepsis (2-4). This vaccine was also used in the phase I clinical study in human subjects where these subjects were actively immunized with the vaccine (1).
Although the dLPS-J5/OMP vaccine demonstrated greater than 20 fold IgG antibody response to the core glycolipid structure of lipopolysaccharide in rabbits, mice and rats, human volunteers developed only a 2-3 fold increase above baseline antibody titers (1). The antibody response was polyclonal with generation of both IgM and IgG antibodies that persisted for at least 12 months (4).
Furthermore, previous passive protection studies had indicated that protection against lethal sepsis was dependent on the concentration of the antibody passively administered. It is also known that an immunogenicity to an antigen can be enhanced by administering the antigen in combination with an adjuvant. Examples of commonly used adjuvants in vaccine preparations include aluminium potassium sulfate, Freund's incomplete adjuvant, Freund's complete adjuvant, alum, synthetic polyribonucleotides and bacterial lipopolysacharides.
Bacterial DNA and synthetic oligodeoxynucleotides (ODN) that contain immunostimulatory unmethylated CpG motifs (CpG ODN) are potent TLR9 agonists (5-6) and have been shown to be potent B cell activators and effective immunoadjuvants when combined with a wide variety of types of antigens, including peptide-based vaccines (7). The CpG motifs also promote a Th1 type immune response which may further promote a combined innate and adaptive immune response essential to resist microbial invasion and promote antibacterial defense mechanisms (8). Additionally, these synthetic oligodeoxynucleotides have potentially benefited patients with asthma, enhance innate host defenses against neoplasia (9-10), and improve human vaccine responses (11). Despite the efficacy of the CpG oligodeoxynucleotides to function as an immunoadjuvant, to date CpG oligodeoxynucleotides have been used as vaccine adjuvants with primarily protein, protein/polysaccharide conjugates and with DNA vaccines (7, 9-11).
Thus, prior art is deficient in a vaccine that elicits a high antibody titer to offer protection against a wide array of Gram negative bacteria as well as monoclonal antibodies to treat infection by such bacteria. The current invention fulfils this long standing need in the art.